1. Field of the Invention
Embodiments of the invention relate to a display device, and more particularly, to a display device and a method of driving the same having wide and narrow viewing modes. Although embodiments of the invention are suitable for a wide scope of applications, they are particularly suitable for providing a display device and a method of driving the same that provide convertibility between wide and narrow viewing angle modes.
2. Discussion of the Related Art
In general, a liquid crystal display (“LCD”) device, which functions as an image display device, includes a first substrate, a second substrate, and a liquid crystal layer. The first and second substrates face each other with a space therebetween, and the liquid crystal layer is interposed between the first and second substrates. An LCD device uses optical anisotropy and polarization properties of liquid crystal molecules to display images. The LCD device includes at least one polarizer on the first and second substrates. Light vibrating a predetermined direction can only pass the polarizer such that the polarizer produces a polarized light.
Viewing angle is an important factor for an LCD device. Thus, the LCD device having a wide viewing angle has been suggested. For example, a twisted nematic (“TN”) liquid crystal cell and a compensation film are used for the LCD device to obtain a wide viewing angle.
FIG. 1 is an exploded perspective view of a wide viewing angle LCD device including a TN liquid crystal cell and a uniaxial retardation film according to the related art. In FIG. 1, a wide viewing angle LCD device 10 includes a TN liquid crystal cell 15, two uniaxial retardation films 13, a first polarizer 11 and a second polarizer 17. The two uniaxial retardation films 13 are disposed on the TN liquid crystal cell 15. The first polarizer 11 is disposed on the uniaxial retardation films 13, and the second polarizer 17 is disposed under the TN liquid crystal cell 15. Thus, the two uniaxial retardation films 13 and the TN liquid crystal cell 15 are disposed between the first and second polarizers 11 and 17.
Such an LCD device having a TN liquid crystal cell has a narrow viewing angle, and luminance of such an LCD device depends on viewing positions of a user. This problem is resulted from refractive index anisotropy of liquid crystal molecules in the TN liquid crystal cell, although the viewing angle is compensated to some extent by disposing the two uniaxial retardation films 13 between the first polarizer 11 and the TN liquid crystal cell 15.
Polarized light, which is perpendicularly incident into the uniaxial retardation film, is not changed by the uniaxial retardation film. However, polarized light, which is obliquely incident into the uniaxial retardation film, is changed by the uniaxial retardation film. Thus, when the polarized light is perpendicularly incident into the two uniaxial retardation films 13, polarizing state of the perpendicularly incident light is not changed by the two uniaxial retardation films 13. In addition, when the polarized light is obliquely incident into the two uniaxial retardation films 13, there is a change in polarizing state due to the two uniaxial retardation films 13. The narrow viewing angle of the LCD device having the TN liquid crystal cell 15 is improved to some extent by controlling a double refraction index of the two uniaxial retardation films 13. Accordingly, the LCD device 10 in FIG. 1 has an improved viewing angle; however, such an LCD device does not provide multi-viewing modes and does not have convertibility between wide and narrow viewing modes.
FIG. 2 is an exploded perspective view of an LCD device having convertibility between wide and narrow viewing angle modes according to the related art. In FIG. 2, an LCD device 50 having the convertibility between the wide and narrow viewing angle modes includes a wide viewing angle mode liquid crystal cell 55, an auxiliary parallel alignment cell 53, and first and second polarizers 51 and 57. The first and second polarizers 51 and 57 are disposed on outer surfaces of the wide viewing angle mode liquid crystal cell 55 and the auxiliary parallel alignment cell 53, respectively.
An alignment direction of the auxiliary parallel alignment cell 53 is parallel to the optical axis of the first polarizer 51, and liquid crystal molecules in the auxiliary parallel alignment cell 53 are aligned parallel to each other, not has a twisted shape. The LCD device 50 including the auxiliary parallel alignment cell 53 produces images that have a clear color change, not color deterioration. In addition, the LCD device 50 including the auxiliary parallel alignment cell 53 has the narrow viewing angle on left and right sides and upper and lower sides.
Accordingly, the LCD device 50 including the auxiliary parallel alignment cell 53 can be convertible between the wide and narrow viewing angle modes. When voltage is not applied into the auxiliary parallel alignment cell 53 or voltage below a threshold is applied into the auxiliary parallel alignment cell 53, the LCD device 50 is in a wide viewing angle mode. In addition, when voltage above the threshold is applied into the auxiliary parallel alignment cell 53, the LCD device 50 is in a narrow viewing angle mode.
In more detail, when voltage is not applied into the auxiliary parallel alignment cell 53 or voltage below a threshold is applied into the auxiliary parallel alignment cell 53, the alignment direction of the auxiliary parallel alignment cell 53 is the same as the optical axis of the first polarizer 51. Accordingly, light passing the wide viewing angle liquid cell 55 passes the first polarizer 51, and the LCD device 50 provides a wide viewing angle. However, when voltage above the threshold is applied into the auxiliary parallel alignment cell 53, the liquid crystal molecules in the auxiliary parallel alignment cell 53 is rearranged to be perpendicular such that the viewing angle on sides is deteriorated. Accordingly, the LCD device 50 provides a narrow viewing angle.
In any event, the above-mentioned cell does not perfectly prevent producing images on sides. It can change phases of light but cannot block light. Accordingly, images are displayed on sides of the LCD device, and person on sides still can observe the images. As such, the LCD devices according to the related art fail to provide sufficient privacy of a user, even in a narrow viewing angle mode.